Regarding:

"If a sales tax of $1 per unit is imposed on consumers, what is the revised demand curve? Explain why the demand curve changes but the supply curve does not change. Explain intuitively why the demand curve shift left = shifts down."

I am having difficulty answering the last sentence of this question.  How much detail do I need to go into?  Is it enough to simply say that this is the case because demand is a downward-sloping curve?

[NEAS: Sample wording: If consumers buy quantity Q at a price P before the sales tax, they buy quantity at a price P – 1 after the tax. Say how this moves the curve.]